Alkylation



Patented Mar. 6, 1945 2,370,171 ALxYLATroN Ernest W. Bowerman, Baytown,Tex., asslgnor to Standard Oil Development Company, a corporation ofDelaware Application July 27, 1942, serial No. 452,421

(ci. 26o-683.4)

6 Claims.

The present invention is concerned `with a process for the alkylation ofisoparainic hydrocarbons with clefinic hydrocarbons. It is primarilyconcerned with an improvement on the two-stage alkylation processwherein olenic hydrocarbons are selectively absorbed in sulfuric acidfrom admixture with parafflnic hydrocarbons in one stage and the acidabsorbed olenic hydrocarbons are reacted under alkylating conditionswith isoparaffinic hydrocarbons in the second zone. The improvementinvolves the removal of oleflns, polymer oils, alkyl sulfates and othercorrosive or potentially corrosive acid re action products from theunabsorbed parafnic hydrocarbons discharged from thev absorption stageand the conversion of these constituents into an additional quantity ofgood quality alkylate (a saturated, high-octane-number, hydrocarboncondensation product) It is well known in the art that low boilingisoparains can be reacted with low boiling oleiinic hydrocarbons in thepresence of concentrated sulfuric acid to form an alkylatehaving a highoctane number. Usually this reaction is carried out in a single-stagereaction system which is commonly called a single-stage process. In thistype of operation it is common practice to blend the isoparaiflnic feedstock (which is predominantly isoparaflin but may contain a small amountof normal paraffin) with the olenic feed stock which comprises a mixtureof oleflns, isoparafllns and normal parailins, and the blend iscontacted with concentrated sulfuric acid under alkylating conditions.In this manner, the

normal parailln contained in the olenic feed stock passes through thesystem as a diluent and it is finally segregated from the alkylate andthe unreacted isoparain by distillation means. The objectionable featureto this type of process is the presence of normal parafns in thereaction mixture which tends to lower the yield and octane number of thealkylate product boiling in the gasoline boiling range. In general, thistendency becomes greater as the concentration of normal paralllnsincreases. Since the olenic feed stock is the principal source of thenormal parafns in the reaction mixture, it is evident that the norma1paraflln content of this stock limits the extent to which the isoparailnconcentration can be built up in the reaction mixture While maintainingpractical feed rates to the singlestage alkylation system.

Modications of the single-stage system have been devised. Thesemodiiications employ the same basic principles used in the single-stagealkylation process; hence they have the same objectionable feature, thepresence of relatively high concentrations of normal paralns in thereaction mixture. One modification consists of employing a multiple ofalkylation reactors in parallel hook-up. In this operation, thehydrocarbon feed stock streams are supplied with sepa. rate portions ofthe same going to the various reactors. Another modification of thesinglestage process now in common use consists of a multiple ofalkylation reactors and settling zones alternately spaced in serieshook-up. In this setup, all of the isoparaffin feed stock is generallyintroduced into the rst reactor of the series and it flows inconsecutive order through all of the reactors' and settling zones in theseries.-

The oleiinic feed stock, onthe other hand, is divided into as manystreams as there are reactors in the system so'that a separate stream ofthe fresh oleilnic feed stock may be introduced intol each reactor.Although not absolutely essential, it is customary to employ andmaintain separate bodies of acid catalyst for each reactor in thesystem. Each reactor, of course, is provided with means for controllingthe reaction temperature as well as means for securing and maintainingintimate contact between the acid catalyst and the hydrocarbonreactants. The advantage of this modification is that it provides ameans of maintaining. a higher concentration of isoparaffins in thereaction mixture than can be secured with the same quantity ofhydrocarbon reactants in a single reactor system.

The so-called two-stage process of alkylating isoparafilns with olenshas been devised to obviate the objectionable feature of introducingsubstantial quantities of norma1 parafns into the reaction mixture,which is common to the single-stage process. The two-stage processconsists first of absorbing the olens from the olefinic feed stock inconcentrated sulfuric acid and then of charging the; acid extract to analkylation reactor wherein it is contacted with an isoparailin andadditional acid of alkylation strength and under alkylation conditionsto produce saturated, high-octane-number hydrocarbon condensationproducts, commonly known as a1- kylate. The virtue of the two-stageprocess lies 4 in the fact that, by excluding from the alkylation stagethe normal paraillns usually present in the oleilnic charge stock, it ispossible to obtain a much higher isoparafrin concentration in thehydrocarbon phase in the alkylation reactor than itis possible to obtainin the single-stage process with essentially the same auxiliarydistillation capacities. It has been demonstrated that the higherisoparatiin concentration, which prevails ln the hydrocarbons in thereactor when the twostage process is used, causes the octane number ofthe aviation gasoline fraction of the alkylate to be 1 or 2 octanenumbers higher than that produced on a single-stage unit from the samefeed stock and with the same operating conditions.

In connection with the two-stage alkylation process, it has been foundthat the operating conditions used for the absorption stage have adecided influence on the yield and quality of the alkylate whiclrissubsequently produced with the extract, and on the acid replacementrequirements for the entire process. It has been demonstrated that it isbest to operate the absorption stage at low temperatures, for example to35 F., for absorbing butylenes; this keeps undesirable side reactions,such as polymerization, Ormandy-Craven type reactions, and oxidationreactions at a minimum. Likewise,l it has been demonstrated that theretention time of the extract in thev absorber should be low, and adownflow jet absorber that sprays acid down through a continuous risinghydrocarbon phase has been used to provide a condition which allows ashort extract retention time. It has further been demonstrated that itis highly desirable to absorb the olen in an extract rather than in puresulfuric acid, and it has been shown that it is necessaryto keep themolecular ratio of sulfuric acid to olefin in the extract phase at adenite maximum value. If acid to olen ratios higher than this maximumvalue are allowed to exist in the extract phase, undesirable sidereactions are accelerated.

The necessity of limiting the molecular ratio of acid to oleiin in theextract phase at a maximum value introduces certain operating problemswhich must be circumvented if the maximum advantage of the two-stagealkylation process is to be realized. For example, in applying thetwo-stage process to normal butylenes alkylation, it is necessary tolimit the sulfuric acid-to-butylene molecular ratio at a maximum valueof 1:1. Such a ratio permits the formation of some dibutyl sulfatos.These sulfatos are more soluble in the liquid hydrocarbon phase than inthe extract and as a consequence they are carried out of the absorber assolute in the residual hydrocarbon phase. Other constituents besidesparaffins and some unabsorbed butylenes that are found to be present inthe residual hydrocarbon in small concentrations are: polymers,hydropolymers, and sulfur dioxide. These materials must be removed fromthe residual hydrocarbon leaving the absorber before it can be used inother renery operations or before it can be used for blending intogasoline stock. In addition, these hydrocarbon materials represent asizable amount of potential alkylate which would be lost unless thematerials are recovered and converted to alkylate in some manner.

One method proposed for removing side reaction products from theresidual butane leaving the absorption stage is to distill the butane,removing the low boiling hydrocarbons as an overhead stream and removinga bottoms stream containing the polymers, hydropolymers, and alkylsulfatos. This bottoms stream is then charged to the alkylation stagealong with the extract. The overhead stream is ready for use aftercaustic and water washing. The trouble with this procedure is that thealkyl sulfate present in the absorber residual hydrocarbon is partiallydecomposed at the temperature maintained in the still bottoms. Theproducts of these decompositions are sulfuric acid, polymers, and sulfurdioxide andwater. 'I'he sulfuric acid and the wet sulfur dioxide areboth corrosive to steel equipment, and the fact that sulfuric acid islost as sulfur dioxide and water causes the acid requirements for theover all two-stage alkylation process be high.

Another method of handling the residual hydrocarbon stream leaving theabsorber which is an improvement over the aforementioned procedure hasbeen proposed.- In this case the residual hydrocarbon phase leaving theabsorber is charged to an evaporator wherein the low boilinghydrocarbons are removed as vapor, care being taken to prevent thetemperature of the nonvolatile components from rising above 70 F. Atthis temperature the thermal decomposition of the alkyl sulfates isminimized. The nonvolatile stream from the evaporator is then recycledto the absorption stage. This practice of recycling tre evaporatorbottoms back to the absorber represses the formation of neutral sulfuricacid esters because of the mass action eiIect on the equilibrium:

azsoi-g-rnsoizzzRHsoi When using this method of handling the residualhydrocarbons leaving the absorption stage, it is necessary to condensethe vaporized hydrocarbon stream, caustic wash and Water wash it toremove sulfur dioxide before it can be used in the other renery streams.Furthermore, a small amount of polymers are formed in the absorber stageeven though the olenie feed stock does not contain iso-olens, forexample, isobutylene, and these polymers 'would not be vaporized in theevaporator and as a result these high boiling constituents would need tobe removed from the absorption system, otherwise a build-up of this typeof material would occur.

I have now discovered a more simple means for handling the residualliquid hydrocarbon phase which leaves the absorption stage of thetwo-stage alkylation process. In accordance with my invention theresidual hydrocarbon leaving the absorber is contacted with sulfuricacid of alkylating strength in the presence of an isoparafiin and underalkylation conditions. This treatment causes the alkyl sulfates, anyunabsorbed olefins, and olen polymers to react with the isoparaiiin toproduce alkylate. This alkylate is about equal in quality to thatproduced in the single-stage alkylation process and it is only slightlyinferior to the alkylate produced in the regular alkylation stage of thetwo-stage alkylation process. This new alkylation operation may becarried out in a separate and independent system from that of thetwo-stage process; however, it is preferable to have the two systemsintegrated so that the hydrocarbon product stream (comprising alkylateand unreacted isobutane) from the alkylation stage of the two-stagesystem becomes the principal source of isobutane for the auxiliaryalkylation system.

The process of this invention may be more clearly understood byreference to the attached drawing which is a diagrammatic flow plan of apreferred embodiment of this invention. For purpose of description it isassumed that the olefin feed stock is a normal refinery butane fractionfrom which all isobutylene vhas been removed, land which is comprised ofnormal butyleues, isobutane and normal. butane. Itis also assumed thatthe iscbutane feed stock is comprised primarily or isobutane but that itdoes contain some normal butane. 'I'he catalyst is assumed to besulfuric acid of allwlation strength. preferably between 90 and 98 percent strength by titratable acidity.

In this embodiment, liquefied butylene feed stock is precooled to atemperature in the range between about 20 F. and 35 F. by means ofcooler I in line 2 before being introduced into absorber 3 at a pointnear its bottom. Absorber 3 is preferably a closed vertical towerequipped with a conical bottom and provided with a downwardly directedspray header l located at a point near the top of the tower and throughwhich acid-butylene extract is introduced into the absorber. As thebutylene feed stock flows upwardly through absorber 0, a large portionof the butylenes contained in the feed stock is absorbed by thedownwardly flowing acid-butylene extract introduced through spray headerl. The hydrocarbons in the butylene feed stock which are not absorbed bythe acid in absorber I are withdrawn from the absorber by means of lineE in which is located control valve 8. The acidbutylene extract iswithdrawn from absorber 3 by means of line 'I which is equipped withpump l and cooler l. Make-up acid, preferably oi' alkylation. acidcatalyst composition, is introduced into the stream of acid-butyleneextract ahead of pump l by means of line Il and the mixture is passedthrough cooler 9 wherein suiiicient refrigeration is supplied to controlthe temperature in the absorber within the range between about 20 F. and35 F. The stream leaving cooler 8 is divided with one portion beingdiverted to the main alkylation system through line II, and the otherportion being recycled to the absorber 3 by means of line I2 whichcommunicates with spray header l. The quantities of butylene feed stock,make-up acid, and recycled acid-butylene extract which are fed intoabsorber 3 are adjusted so that the molecular ratio of acid to butylenein theacid phase does not exceed 1:1. It is preferable to control theacid-butylene extract recycle rate so as to allow complete coalescenceof extract in the bottomof the absorber. 'I'he absorber system isoperated at a pressure suiiiciently high to maintain the hydrocarbons inthe liquid phase and the pressure in the system is preferably greaterthan the pressure maintained in the alkylation system-which will bedescribed in a subsequent part of this specification. The absorbersystem is designed so that the extract is not retained in the systemmore than 20 to 40 minutes.

The main alkylation reaction system, comprising alkylation reactor I4and reaction-mixturerecycle line I5 which is equipped with cooler I6,and a recycle pump I1, is filled with alkylation reaction mixturecomprising isobutane, acid-butylene extract, alkylation acid catalystand alkylate product. This reaction mixture is continuously circulatedin the alkylation reaction system and it is maintained under conditionsof temperature, pressure, catalyst strength and proportion of reactantswhich are known to be favorable for promoting the alkylation ofisobutaue with acidabsorbed-butylene extract and which do not constitutea part of this invention. However, for purpose of clarification itisenumerated that the reaction mixture should contain at least 40 volumeper cent acid catalyst and the hydrocarbon phase should contain at leastvolume per cent of isobutane, preferably abovev volume per cent. The

reaction mixture should be maintained at a tem-` action systempreferably at a point in reactionmixture-recycle line Ii ahead of coolerI8 and. recycle pump I1. Isobutane feed stock precooled to a temperaturein the range between 30 F. and 50 F. by means of cooler I8 in line I9 isalso introduced into recycle line I5 preferably at a point ahead ofcooler I8 while fresh make-up sulfurie acid of alkylating strength,preferably of` to 98 per cent titratable acidity. is introduced intoline I5 at a point between cooler I6 and recycle pump I'I by meansofline 20. Alkylation catalyst separated from reaction mixture divertedfrom the system and segregated for product recovery is recycled to thesystem by means of valve controlled line 2| which is in communicationwith line I5 ahead 'of pump I1. The hydrocarbon reactants, fresh acidand recycled acid catalyst introduced into line I5 are intimately mixedwith one another and with the circulating reaction mixture as they passthrough pump I1 and jet header 22 located in the bottom of reactor I4and in communication with line I5. A portion of the reaction mixturedischarged from reactor I4 through recycle line I5 is diverted throughvalve controlled line 23 to an auxiliary alkylation system which isdescribed hereinafter.

In a conventional two-stage alkylation process such as the one which hasjust been described the usual procedure is to pass the reaction mixturewithdrawn from the main alkylation system, such as by means vof line 23,directly to an acid separator, such as separator 32. wherein the acidcatalyst is separated from the hydrocarbons and the latteris segregatedfor the recovery of alkylation product. In accordance with my invention,this stream of hydrocarbons segregated for alkylate product recovery maybe introduced into an auxiliary alkylation reactor wherein it iscontacted under alkylation conditions and in the presence of sulfuricacid catalyst with the hydrocarbon stream withdrawn from absorber 3 bymeans of line 5 to eiect alkylation of the unreacted isobutane presentin the stream of hydrocarbons segregated for alkylate product recoverywith the butylenes, butylene polymer oil and the alkyl sulfates presentin the hydrocarbon stream withdrawn from absorber 3. It is generallydesirable to pass the reaction mixture to an acid separator, such asindicated by numeral 5l, to separate an acidphase from a hydrocarbonphase and pass the hydrocarbon phase into line 25 and withdraw the acidphase to line I0. It is sometimes desirable to withdraw from the systema portion of the acid separated in vessel 54 by outlet-55 and to add anequivalent amount of fresh acid to auxiliary alkylatcr vessel 24 byinlet 58. It will be understood that this is an optional operation andthat if desired the mixture may be passed directly from unit il intoline 25, bypassing the separating stage. However, in accordance with apreferred embodiment of my invention, the reaction mixture (comprisingacid catalyst and hydrocarbon) system. Similarly,

ilowing through line 23 is introduced directly into an auxiliaryalkylation reaction system which comprises alkylation` reactor 24 andalkylationreaction-mixture recycle line 25 which contains cooler 26 andrecycle pump 21. Line 23 preferably communicates with line 25 at a pointahead of cooler 26. This stream of reaction mixture diverted from themain alkylation reaction system becomes the principal source of acidcatalyst and isobutane for the auxiliary alkylation reaction the streamof non-acidsystem by means'of line 2i and with the auxiliary alkylationsystem' by means of line 28.

' The hydrocarbon phase separated in acid separator I2 is withdrawn bymeans of line 38, is admixed with dilute caustic, introduced by means ofline 31, and the mixture is passed through incorporator 38 before beingintroduced into caustic separator 3l. In caustic separator, the causticabsorbed hydrocarbons withdrawn from absorber 3 and introduced throughline 5 into recycle line 25 ahead of cooler 26 becomes the source ofolefins for the auxiliary alkylation reaction sys-- tem. As previouslystated, this stream of hydrocai-bons contains a small amount ofunreacted be introduced into the auxiliary alkylation systemby means ofvalve controlled line 28 which communicates with line 25 ahead of pump21.

-Intimate contact between the hydrocarbon reactants and the acidcatalyst is eiected as the mixture passes through recycle pump 21 andJet header 29, located in the bottom of reactor 24, and in communicationwith recycle line 25. Part of the reaction mixture leaving the auxiliaryreand a hydrocarbon phase.

is settled and separated from the hydrocarbons, the hydrocarbons beingdischarged through line 40 and the caustic beingdischarged through line4 i. As the hydrocarbons ilow through line 40 they are admixed withwater introduced by means of line 42 and the mixture passes through anlncorporator 43 before being introduced into water separator 44 forseparation into a water phase The water phase is withdrawn through line45.

The hydrocarbon phase is withdrawn from water separator 44 by means ofline 46 and it is introduced into distillation unit 41 where it isseparated into a butane fraction and an alkylate fraction. The alkylatefraction is withdrawn .as a residual material through line 48 and it maybe further processed in any marmer desired. The butane fraction isremoved as an overhead pro duce through line 49 and it is introducedinto distlllation unit 50 wherein it is split into'an isobutane fractionand anormal butane fraction.

actor 24 through line 25 is diverted to acid settler to 40:1. Theconditions of temperature and acid strength employed in this auxiliaryalkylation system are substantially the same as those employed in themain alkylation system. The pressure should be sufllciently high tomaintain liquid phase but should not be as high as the pressuremaintained in the main aikylation system for pur.y pose of promotingflow of reaction mixture from the main alkylation system to theauxiliary alkylation system. Because of the normal butane contained inthe stream of hydrocarbons introduced from absorber 3, the concentrationof isobutane in the hydrocarbon phase of the reaction i mixture will besomewhat lower'in the auxiliary reactor than in the main reactor; but inthe interest of obtaining a reasonable yield of good quality alkylate,this isobutane concentration should not be allowed to become less thanV30 mol per cent. If necessary for the maintenance of a suitableisobutane concentration in vessel 24, fresh isobutane feed stock whichhas been introduced by inlet I9 and passed through cooler I8 may bewithdrawn through branch 51 and added to the stream circulating throughline 25.

The stream of reaction mixture diverted from the auxiliary alkylationreaction system by ineans Example In this experiment an apparatus and acontinuous operation of the type hereinbefore described was employed.The butylene charge stock v consisted of 20 mol per cent normalbutylenes, 12

mol per cent isobutane andv 68 mol per cent normal butane. On the basisof each mols of the butylene charge stock introduced into the acidabsorption system, this feed stock was contacted with 1480 lbs. ofsulfuric acid alkylation catalyst of 91 per cent titratable acidity inthe presence of recycled acid-butylene extract. This quantity ofalkylation catalyst was suiiicient to furnish about 1.0 mol of H2804,based on titratable acidity, for each mol of butylenes absorbed. With ahydrocarbon contact time of about 40 of line 30 and passed to acidseparator 32 is settion and alkylation systems by means of line I I andpump 35, which is located in line III. Line Il is connected with themain alhlation reactor minutes in the absorption zone, the acid phaseabsorbed 13.8 mois of butylenes, leaving dissolved in the hydrocarbonphase 3.0 mois of unreacted butylenes, 2.8 mols of butylenes in the formof di-y butyl sulfate and 0.4 mol of butylenes in the form of polymeroil. The absorption operation was carried out at a temperature of 25 F.under a pressure of 100 pounds per square inch gauge, using an extractretention time in' the absorber of about 40 minutes.

'I'he acid extract containing the 13.8 mois of absorbed butylenes(derived from the 100 mols of butylene feed stock charged to theabsorber) was withdrawn from the absorption system and introduced intothe ma'm alkylation system along with an isobutane feed stock containing71.6 mols of isobutane and 10.9 mois o f normal butane. These streamswere introduced into the circulating stream of alkylation reactionmixture which was withdrawn from the top of the main reactor andrecycled to the bottom of that reactor. 'Ihere were also introduced intothis stream of circulating alkylation reaction mixture 1,060 pounds of97.0 per cent strength sulfuric acid and a sufficient quantity ofalkylation acidcatalyst of 91 per cent titratable acidity (which waswithdrawn from the acid settler following the auxiliary alkylationreactor and which was recycled to this main alkylation system) tomaintain in the main alkylation reactor a volume ratio of acid phase tohydrocarbon phase of about 1:1. This alkylation operation was carriedout at a temperature of 35 F. under a pressure of about "l pounds persquare inch gauge, with the volume ratio of recycled alkylation reactionmixture to the isobutane feed stock being in the order of :1. Underthese conditions of operation, 13.1 mols of butylenes out of the 13.8mols of butylenes charged in the form of acid extract were converted toalkylate having an average molecular weight of 114.

The stream of reaction mixture IWithdrawn from the main alkylationsystem and introduced into the auxiliary alkylation system was comprisedof about equal volumes of acid phase and hydrocarbon phase. Thehydrocarbon phase contained 58.5 mols oi' isobutane, 10.9 mols of normalbutane and 13.1 mols of alkylate. This stream of reaction mixture wasintroduced into the emulsion recycle line of the auxiliary reactor alongwith the residual butane stream withdrawn from the absorption system. Inaddition, a sufiicient quantity of alkylation acid catalyst waswithdrawn from the acid settler and recycled to the emulsion recycleline of the auxiliary alkylation reaction system to maintain about 1:1volume ratio of acid phase to hydrocarbon phase in the auxiliaryreactor. The residual butane withdrawn from the absorption systemcontained 12 mols of isobutane, 68 mols of normal butane, 3 mols ofunreacted butylenes, 2.8 mols of butylenes in the form of dibutylsulfate and 0.4 mol of butylenes in the forni of polymer oil. In thisauxiliary reactor, the alkylation reaction was carried out at atemperature of 35 F. under a pressure of 40 pounds per square inchgauge. The emulsion recycle ratio employed in this system was about 20volumes of reaction mixture per volume of hydrocarbons introduced intothe system. The reaction mixture discharged from this auxiliaryalkylation system was passed to an acid settler wherein the hydrocarbonphase was separated from the acid phase. As previously stated, the majorportion of the acid phase was recycled to the absorber. the mainalkylation reactor and the auxiliary alkylation reactor; however, aquantity of this acid equivalent to the make-up acid introduced into themain alkylation reactor was discarded. This discarded acid contained acarbonaceous diluent material equivaient to 1 mol of butylenes.

Distillation of the hydrocarbon phase leaving the acid separatorshowedit to contain 64.6 mols of isobutane. 78.9 mols of normal butene,and 19 mols of alkylate. This alkyla was found to have a bromine numberof 0. showing it to be free of unsaturates. Prolonged treatment of thealkylate with either a hot acidic or a hot basic aqueous solution failedto give any hydrolytic products, indicating that all the alkyl sulfatesand other side reaction products had been removed from the hydrocarbonmixture. This alkylate was found to contain 92.9 volume per cent ofmaterial boiling below 320 F. which had an A. S. T. M. octane number of94.8; whereas, an alkylate prepared from a single-stage process madeunder conditions comparable to those employed on the auxiliaryalkylation reactor contained only 89.6 volume per cent of materialboiling below 320 F. which had an octane number of only 93.7. In aseparate operation wherein the hydrocarbon product leaving the mainalkylation reactor was segregated, it was found that the alkylate formedin this main alkylation reactor Was of exceptionally high qualitycontaining 94.5 volume per cent of material boiling below 320 F. andhaving an octane number of 95.3.

It is obvious to those skilled in the art that many` modifications ofthis invention may be employed without departing from the spirit andscope of the invention. For example, with modil fications obvious tothose skilled in the art, the

process of this invention may be adapted for use in the alkylation ofisobutane with pentylenes or propylene or in the alkylation ofisonentane with butylenes or propylene.

I claim:

. 1. In a two-stage alkylation process consisting of an absorption zone,wherein a mixed feed stock containing olefins and paraflins is contactedwith sulfuric acid to form an extract phase containingv the bulk of theolefins and a rafllnate phase containingparailins, some unabsorbedoleflns, some olefin polymer oil and some alkyl sulfates, and a mainalkylation zone, wherein the said extract is reacted with an isoparaiiinunder alkylation conditions, the improvement which comprises withdrawingreaction mixture from the main alkylation zone and passing it to an acidsettler wherein the mixture is settled and separated into an acid phaseand a hydrocarbon phase, withdrawing the hydrocarbon phase from saidacid settler and passing it to an auxiliary alkylation zone, separatelywithdrawing the acid phase from the said acid settler, discarding fromthe system a portion of the said withdrawn acid and recycling thebalance of the said withdrawn acid to and distributing it between theabsorption zone and the main alkylation zone, introducing fresh make-upacid into the main alkylation zone in an amount equivalent to the aciddiscarded from the system, withdrawing raffinate from. the saidabsorption zone and passing it to said auxiliary alkylation zone whereinit is contacted under alkylating conditions and in the presence ofsulfuric acid alkylation catalyst with the hydrocarbon phase introducedtherein from the said acid settler to eiect alkylation of unreactedisoparain present in the hydrocarbon phase with oleiins, olen polymeroil and alkyl sulfatos present in the raiinate, withdrawing reactionmixture from said auxiliary alkylation zone and passing it to an acidseparator wherein the mixture is settled and separated into an auxiliaryacid phase and a hydrocarbon phase. withdrawing the hydrocarbon phasefrom said acid separator, separately withdrawing the auxiliary acid fromthe said acid separator, discarding a portion of the auxiliary acidwithdrawn from said acid separator and recycling the balance of thatacid to the auxiliary alkylation zone, and introducing into theauxiliary alkylation zone make-up acid equivalent sulfuric acid to forman extract phase containing the bulk of the oleiins and a raiilnatephase containing the parafns, some unabsorbed oleiins, some olefinpolymer oil, and some alkyl sulfates,

and a main alkylation zone, wherein the said extract is reacted with anisoparaiiin underA alkylation conditions, the improvement whichcompriseswithdrawing railinate from the absorption zone and passing it tdanauxiliary alkylation zone, withdrawing reaction mixture from the mainalkylation zone and passing it to'said auxiliary alkylation zone whereinit is reacted with p the raffinate under conditions of alkylation and inthe presence of sulfuric acid catalyst to eiect alkylation of unreactedisoparain present in the reaction mixture with oleflns, olefin polymeroil and alkyl sulfates present inthe rainate, withdrawing reactionmixture from said auxiliary alkylation zone and passing it to an acidsettler wherein the mixture is settled and separated into an acid phaseand a hydrocarbon phase, withdrawing the hydrocarbon phase from saidacid settler, separately withdrawing the acid phase from the acidsettler, discarding from the system a portion of the withdrawn acid andrecycling the balance of the acid to and distributing it between theabsorption zone, the main alkylation zone and the auxiliary alkylationzone, and introducing fresh make-'up acid into the main alkylation zonein an amount equivalentto the acid discarded from the system.

3. In a two-stage alkylation process comprising an absorption zone wherea mixed feed stock containing olefins and parailins is contacted withsulfuric acid to form an extract phase and a raffinate phase and a rstalkylation zone wherein the said extract is reacted with an isoparafnunder alkylating conditions, the improvement comprising withdrawing theraffinate from -the absorption zone and passing it to a secondalkylation zone, withdrawing the alkylation mixture from the firstalkylation zone and passing it to the second alkylation zone where it isallowed to react with the rafiinate under alkylation conditions,removing reaction mixture from said secv ond alkylation zone, andseparating a hydrocarbon phase therefrom.

4. In a two-stage alkyiation process comprising an absorption zone wherea mixed feed stock containing oleflns and paraillns is contacted withsulfuric acid to form an extract phase and a raffinate phase and a nrstalkylation zone wherein the said extract is reacted with isoparafilnunder alkylating conditions, the improvement comprising withdrawing therafiinate from the absorption zone and passing it to a second alkylationzone, withdrawing from the first alkylation zone iiuid which has takenpart in the alkylation reaction and passing at least'I a portion thereof\to the second alkylation zone, where it is allowed to react with theraiiinate under alkylation conditions.

5. In a two-stage alkylation process comprising' an absorption zonewhere a mixed feed stock containing oleiins and paraiilns Iis contactedwith sulfuric acid to form an 'extract phase and a raffinate phase and afirst alkylation zone wherein the said extract is reacted withisoparaiiin under alkylating conditions in the presence of sulfuric acidcatalyst, the improvement comprising withdrawing the raflinate from theabsorption zone and passing it to a second alkylation zone, withdrawingfrom the first alkylation zone iiuid which has taken part in thealkylation reaction and separating it by settling into a rst portionincluding a major amount of hydrocarbons and a second portion includinga major amount of acid, passing the rst portion to said secondalkylation zone andreacting it with the ramnate under alkylationconditions.

6. In a two-stage allnrlation process comprising an absorption zonewhere a mixed feed stock containing olefins and paralns is contactedwith sulfuric acid to form an extract phase and a raiilnate phase, anda. rst alkylation zone wherein the said extract is reacted with isoparaflin under alkylating conditions in the presence of sulfuric acidcatalyst, the improvement comprising withdrawing raflinate from theabsorption zone and passing it to a second alky tion zone,`

withdrawing from the first alkylation zone the iiuid which has takenpart in the alkylation reaction and passing it to the second alkylationzone

